I worked in retail and customer service for a LOT of years. Seeing the good the bad and the ugly made me more determined that *I* was going to be different.
When I go into a gas station, grocery store, etc. I always smile at the cashier and say "Hi, how are you?" Just this one tiny thing gets more reactions! In Walmart for back-to-school I shocked the cashier so much, he actually told me it was refreshing to have a customer be friendly and "do my job the same way I do it" and told me it was a pleasure to be my cashier.

It's the southern girl in me, I suspect, to catch more flies with honey. . .but if you are nice first, it's very hard for them to be rude back. Just my 2 cents.